1. Field of the Invention
The present invention relates to integrated optical components and, in particular, to optical components capable of switching and/or attenuating at least one optical channel and performing add or drop functions for optical channels. Particularly preferred implementations facilitate switching and/or attenuating arrays of optical channels.
2. Description of the Related Art
Optical networks are used for wide area and long distance communication, including for the backbone of the Internet. Demand for additional bandwidth in short haul (i.e., metro) and long haul applications continues to grow and a variety of different strategies have been adopted to make optical networks less expensive and more flexible. Optical networks use a variety of components, including add/drop modules, attenuators and optical switches. Generally these components are bulky, expensive and have low levels of integration. The lack of adequate, reliable and cost-effective components has retarded the implementation of optical networks and has limited optical networks to very high traffic systems.
Conventional optical switching proceeds by various methods that include completely mechanical switching, polarization controlled switching, interferometric switching and MEMS switching.
Completely mechanical switching physically moves an input channel and/or an output channel (usually in the form of an optical fiber) with a microelectromagnetic switch (FIG. 1) to alter the state of a switch or to change the coupling between channels. Referring to FIG. 1, a first switching state is indicated at 10 in which fibers representing input channels 1 and 2 are coupled to corresponding fibers representing output channels 1 and 2. The assembly can be switched between the state indicated at 10 in which input 1 is coupled to output 1 and input 2 is coupled to output 2 to either of the states indicated by 12 and 14. State 12 couples input 1 to output 2 and input 2 to output 1 and illustrates the use of the FIG. 1 assembly as a 2xc3x972 switch. Switching is accomplished, for example, by rotating the two input fibers using a microelectromagnetic element. State 14 couples input 1 to output 2 and does not connect output 1 or input 2 to another channel. This 2xc3x972 add-drop switching is accomplished, for example, by linearly translating the two input fibers using a similar microelectromagnetic element. The physical movements required to alter the states or coupling make the switches schematically illustrated in FIG. 1 slow and preclude scaling the switches into an array.
A second type of switching is polarization controlled switching and is illustrated in FIG. 2. Polarization controlled switching uses a polarization rotator whose light transmission is attenuated if followed by a polarizing filter. Polarization controlled switching is polarization dependent. It is preferable for any optical switch to accept light input having an arbitrary polarization. Consequently, polarization controlled switches include components to make the switch insensitive to the polarization of the input light.
A polarization controlled variable optical attenuator (VOA) switch that is insensitive to input light polarization is shown in FIG. 2. Input light 16 passes through a polarizing beam-splitter 18 that separates the input light into two non-overlapping beams of orthogonal polarization light. Each of the separated beams passes through a polarization controlled light switch 20, 22 adapted to the polarization of the separated beams to apply polarization controlled switching to each beam. The beams are provided to another polarizing beam splitter 24 that combines the two beams into a single output. The complexity required to eliminate the polarization sensitivity adds expense. In addition, the polarizing beam splitter and combiner are usually bulk components that are not readily integrated into an array.
FIG. 3 shows an interferometric switch that uses a Mach-Zehnder type interferometer. The illustrated interferometric switch is usually formed as a planar waveguide circuit and includes 2xc3x972 couplers on either end of a pair of interferometric arms. One of the arms has an optical element that is switched thermally or electro-optically to vary the phase delay between the two arms of the interferometer. The 2xc3x972 couplers on both ends of the interferometer arms are precisely fabricated to ensure an exact 50/50% coupling, since any imbalance between the arms manifests itself as an insertion loss as well as a poor extinction ratio or crosstalk. Typical interferometric switches have an extinction ratio or crosstalk of worse than 20 dB. It is difficult to manufacture such interferometric switches economically, especially scaling such switches into an array with many channels.
Another type of optical switch uses microelectromechanical (MEMS) structures to switch optical channels. A common MEMS 2xc3x972 switch is illustrated in FIG. 4, where the input and output channels are optical fibers. A more specific description of this 2xc3x972 switch formed on a silicon on insulator (SOI) substrate is shown in C. Marxer, et al., xe2x80x9cVertical Mirrors Fabricated by Deep Reactive Ion Etching for Fiber-Optic Switching Applications,xe2x80x9d IEEE/ASME Journal of Microelectromechanical Systems, Vol. 6, No. 3, pp. September 1997. Referring to FIG. 4, a MEMS mirror 26 is shown in a first switch position in which input 1 is coupled to output 1 and input 2 is coupled to output 2. In the second switch position indicated by MEMS mirror 28 withdrawn from between the optical fibers, input 1 is coupled to output 2 and input 2 is coupled to output 1.
The MEMS switch system of FIG. 4 is limited in that the diameter of the optical fibers prevents the fibers from being placed close to each other and to the MEMS switching blade. If the fiber tips are not positioned closely together, the light from an input fiber diverges unacceptably before it is captured by the output fiber, resulting in a high insertion loss. It is difficult to taper the ends of fibers consistently. Variations in the taper of the fiber makes the dispersion and the coupling between fibers unpredictable. Another limitation of the illustrated system is that the input and output channels and MEMS structures are oriented in various directions, making it difficult to scale the switch into a linear array on a single wafer.
Single mode optical channels in either optical fibers or planar channels on substrates are usually small, on the order of several micrometers, so that precise positional alignment is required to couple light into and out of such channels. Also, light emitted from such waveguides diverges in a few tens of micrometers so that the working distance between the emitting waveguide and the receiving waveguide is short. The working distance between emitting and receiving channels often needs to be extended to provide sufficient room for switching components between the channels. The conventional method to extend the working distance for switching components is to expand the light beam from the emitting fiber followed by collimating the expanded light with lenses. This not only adds to the complexity and cost of the system but also aggravates the receiving channel""s susceptibility to angular misalignment. In general, the collimator of the receiving channel is precisely aligned positionally and angularly to both the switching mirror and the emitting channel""s collimator. In an array of switches, the tight position and angular tolerances are maintained across the array. Also the pitches of the waveguide and mirror arrays have to be matched to a micrometer or better.
An aspect of the present invention provides an optical component including a waveguide substrate having an edge and having first and second waveguides formed within the waveguide substrate, the first waveguide having a first end on the edge and the second waveguide having a second end on the same edge. A mirror is positioned adjacent to the edge of the waveguide substrate to receive an optical signal from the first end of the first waveguide and direct the optical signal to the second end of the second waveguide in at least one position of the mirror. The mirror is movable to alter the amount of coupling between the first waveguide and the second waveguide.
Another aspect of the present invention provides an optical component including a waveguide substrate having an edge and having first, second and third planar waveguides extending within the waveguide substrate, each of the first, second and third waveguides having an optical path extending through the edge of the waveguide. A mirror is positioned adjacent to the edge of the waveguide substrate. The mirror is spaced from the edge of waveguide substrate, the mirror receiving an optical signal output from the first waveguide and directing the optical signal to the second waveguide in at least a first position of the mirror, the mirror receiving the optical signal and directing the optical signal to the third waveguide in at least a second position of the mirror. The mirror is movable to couple the first waveguide either to the second waveguide or to the third waveguide.
Still another optical component includes a waveguide substrate having an edge and having first, second, third and fourth planar waveguides extending within the waveguide substrate. Each of the first, second, third and fourth waveguides has an optical path extending through the edge of the waveguide. A mirror is positioned adjacent to the edge of the waveguide substrate. The mirror is spaced from the edge of waveguide substrate and receives a first optical signal output from the first waveguide and directs the first optical signal to the third waveguide in at least a first position of the mirror. The mirror receives the first optical signal and directs the first optical signal to the fourth waveguide in at least a second position of the mirror. The mirror receives a second optical signal output from the second waveguide and directs the second optical signal to the third waveguide in at least the second position of the mirror. The mirror is movable to couple the first optical signal to the third waveguide or to the fourth waveguide.
Yet another optical component includes a waveguide substrate having an edge and having first, second and third planar waveguides extending in parallel within the waveguide substrate, each of the first, second and third waveguides having an optical path extending through the edge of the waveguide. A lens is positioned within the optical path of each of the first, second and third planar waveguides. A mirror is positioned adjacent to the edge of the waveguide substrate, the mirror spaced from the edge of waveguide substrate and receiving an optical signal output from the first waveguide and directing the optical signal to the second waveguide in at least a first position of the mirror. The mirror receives the optical signal and directs the optical signal to the third waveguide in at least a second position of the mirror. The mirror is movable to couple the first waveguide either to the second waveguide or to the third waveguide.